Wet venting a Geberit in-wall toilet with washing machine drain

[FerryView]

Hi everyone, I'm new to this forum (but not new to plumbing).

I have attached a pic of my proposed setup for using an additional relief vent to vent an in-wall toilet by Geberit. In this set-up, the relief vent (for the toilet) would also be a wet vent since I am using the vent pipe that is intended to serve the washing machine stand pipe.

In the picture, the Geberit toilet waste comes from the left through a 3 inch pipe, flowing to the right. The distance of that pipe to the waste stack will be about 8 to 9 feet (there is a 3 inch vent at that stack, going through the roof). Because of the 8-9 ft distance, I decided an additional relief vent would be a good idea, and I'm thinking of using the washing machine vent for that purpose, using a 2 inch vent pipe instead of a 1.5 inch vent pipe.

Is the set up shown in the picture correct? Are the correct pipes/fittings being used? The wet vent portion is all 3 inch pipe (like the toilet waste pipe), into which the washing machine's 2 inch pipe drains, and from which the 2 inch vent pipe goes up.

Any advice is appreciated, and thank you for your help!

 

[wwhitney]

Seattle follows the UPC with amendments, and horizontal wet venting is only allowed within a bathroom group, which excludes your washing machine stand pipe. So the arrangement shown doesn't meet the UPC, you need to vent the toilet separately from the laundry drain.

If you're able to flip the standpipe trap and san-tee around (mirror image), then you can use a 2" san-tee and 3"x2" combo for the laundry drain. Upstream of that 3" x 2" combo you could use another 3" x 2" combo for the toilet dry vent. It would rise parallel to your 2" laundry vent to a height of at least 6" above the laundry standpipe; then the two vents could combine.

If the above doesn't work because of the layout of the walls, a floor plan would be helpful to suggest alternatives.

Cheers, Wayne

 

[Sponsor]

 

[FerryView]

Thanks for your response. My understanding is that this is not horizontal wet venting, but vertical wet venting. Does that change you response?

 

[wwhitney]

You raise a good point, but checking the UPC section on vertical wet venting (section 908), it begins "Wet venting is limited to vertical drainage piping receiving the discharge from the trap arm of one and two fixture unit fixtures that also serves as a vent not exceeding four fixtures." And a clothes washer standpipe is 3 DFUS (drainage fixture units), so the vertical laundry drain is excluded from vertical wet venting.

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/9/vents#908.0

Cheers, Wayne

 

[FerryView]

You raise a good point, but checking the UPC section on vertical wet venting (section 908), it begins "Wet venting is limited to vertical drainage piping receiving the discharge from the trap arm of one and two fixture unit fixtures that also serves as a vent not exceeding four fixtures." And a clothes washer standpipe is 3 DFUS (drainage fixture units), so the vertical laundry drain is excluded from vertical wet venting.

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/9/vents#908.0

Cheers, Wayne

Yes, that is true. Aware of that. What I was wondering is whether since this acts as an additional relief vent for the toilet, not the primary vent (which is at the stack) whether it matters that the fixture unit quantity is 1 point over what the Vertical Wet Venting sections allows. Any thoughts?

 

[Terry]

You can't mix a washer into a wet vent situation in Seattle and have it pass an inspection.
The washer is a pumped fixture, unlike a lav where you wash your hands or a shower. When a washer dumps all of the water out, it's totally different.
The codes are there to protect you in that situation, but for that to work, you have to follow the rules.

Area of pipes
1.5" = 1.767"
2.0 = 3.142"
3.0 = 7.069"
4.0 = 12.57"

 

[FerryView]

You can't mix a washer into a wet vent situation in Seattle and have it pass an inspection.
The washer is a pumped fixture, unlike a lav where you wash your hands or a shower. When a washer dumps all of the water out, it's totally different.
The codes are there to protect you in that situation, but for that to work, you have to follow the rules.

I understand that this forum wants to instill in people the need to stick to the code - I get it (I am a lawyer). However, I am reading the code and it is really not that categorical about the situation I am presenting here. My original post, as well as my previous comment, mentioned that this would be a "Relief Vent" for a toilet waste pipe that does in fact have a 3" vent at the 3" stack. I appreciate that wwhitney pointed me to the vertical wet venting section (of which I was already aware), but since this is a "Relief Vent" it is not precisely on point because that section deals with primary venting of fixtures via a wet vent - not with "Relief Vents" that are additional to an existing proper vent, as in my case.

So my questions arose because I also studied section 911 related to Circuit Venting. And subsections 911.4.1 and 4.2, dealing with Relief Vents for circuit vented systems receiving the discharge of toilets, state that:

4.1 The relief vent shall connect to the horizontal branch drain between the stack and the most downstream fixture drain of the circuit vent. The relief vent shall be installed on the vertical to the horizontal branch.

4.2 Fixture Drain or Branch. The relief vent is permitted to be a fixture drain or fixture branch for a fixture located within the same branch interval as the circuit-vented horizontal branch. The discharge to a relief vent shall not exceed 4 fixture units.​

I should also point out that section 912 allows for engineered vent systems that ostensibly may address configurations that the code neither explicitly forbids nor explicitly addresses in any section, so clearly there is some leeway in applying the code.

Now, you can reply by arguing that 911 does not apply to my situation because my situation is not a circuit venting situation; but my reply would be that in that case there are no sections in the code that expressly address my situation, and that 911.4.2 comes closest to addressing "Relief Vents" and is therefore probative to what may be permitted.

It is due to the fact that the code does not address my situation that I came to this forum for input.

Thanks folks!

 

[Terry]

Just for fun, take a look at this properly plumbed and vented back to back toilet installation. This was done to code, and yet it still affects the toilet in the other room. After a while there is almost no water left the the bowl.

 

[wwhitney]

Much as I appreciate a good logical parsing of the plumbing code, you're off base here.

UPC requires a vent for a WC within 6' of developed length of the WC fixture drain (1002.2). There's no provision to extend the distance to the "primary" vent by providing an earlier "secondary vent". The earlier vent within 6' would just be your vent, and the farther vent would be immaterial.

Relief vents don't come into play here, because if you read the section on circuit venting, they are auxiliary vents provided downstream of the primary vent, not upstream of it.

So what's wrong with the solution I suggested? If you provide some details on your layout, we could actually help you.

Cheers, Wayne

P.S. I trust you know your laundry p-trap has to be 6" to 18" above the floor? 804.1.

PPS Someone else helpfully added this picture to my post:

 

[FerryView]

Much as I appreciate a good logical parsing of the plumbing code, you're off base here.

UPC requires a vent for a WC within 6' of developed length of the WC fixture drain (1002.2). There's no provision to extend the distance to the "primary" vent by providing an earlier "secondary vent". The earlier vent within 6' would just be your vent, and the farther vent would be immaterial.

Relief vents don't come into play here, because if you read the section on circuit venting, they are auxiliary vents provided downstream of the primary vent, not upstream of it.

So what's wrong with the solution I suggested? If you provide some details on your layout, we could actually help you.

Cheers, Wayne

P.S. I trust you know your laundry p-trap has to be 6" to 18" above the floor? 804.1.

I think you've answered my questions convincingly with that last posting - that was very helpful. What you said is also interesting - if I go with your suggested configuration, based on what you said (The earlier vent within 6' would just be my vent), does it mean that I could remove the 3" vent (the farther vent) going up through the roof from the stack (it's not being used by any other fixtures), and cap off the stack there?

Yes, I do know about the height requirements of the P-trap. It would be within that range.

Thanks!

 

[wwhitney]

As to removing the 3" vent, it depends on what other vents you have The UPC requires the aggregate area of vents through the roof to be at least as large as the minimum required building drain. Generally for a residence, if you have 3 or fewer toilets, the minimum required building drain is 3" ; if it's 4 or more, it's 4".

So the question is whether you would still have enough other vents through the roof after removing the 3" vent. If you would, then you can remove the 3" vent.

Cheers, Wayne

 

[FerryView]

As to removing the 3" vent, it depends on what other vents you have The UPC requires the aggregate area of vents through the roof to be at least as large as the minimum required building drain. Generally for a residence, if you have 3 or fewer toilets, the minimum required building drain is 3" ; if it's 4 or more, it's 4".

So the question is whether you would still have enough other vents through the roof after removing the 3" vent. If you would, then you can remove the 3" vent.

Cheers, Wayne

I have two toilets; and I have two more vents going through the roof. Both of them are currently 1.5" but I can/will turn at least one of them into a 2" vent. Would that be sufficient? If it is questionable, I won't remove the 3" vent at the stack.

 

[wwhitney]

Area is proportional to the square of diameter, and for this purpose using the nominal diameter should suffice.

3 * 3 = 9
2 * 2 = 4
1.5 * 1.5 = 2.25

So you would need, say (2) 2" vents and a (1) 1.5" vent. The UPC requires a 2" vent for a toilet, which means you should have at least (2) 2" vents (unless the toilets share a vent). If you don't have a third vent, probably easiest to leave the 3" vent.

Cheers, Wayne

 

[FerryView]

Area is proportional to the square of diameter, and for this purpose using the nominal diameter should suffice.

3 * 3 = 9
2 * 2 = 4
1.5 * 1.5 = 2.25

So you would need, say (2) 2" vents and a (1) 1.5" vent. The UPC requires a 2" vent for a toilet, which means you should have at least (2) 2" vents (unless the toilets share a vent). If you don't have a third vent, probably easiest to leave the 3" vent.

Cheers, Wayne

Ok, thanks. Makes perfect sense. I'll leave it in place.

 

[Tuttles Revenge]

Since you're presumably installing this in Seattle. Here is the guidelines for that location.

King County Horizontal Wet Venting Guide